System and method for coding information on a biosensor test strip

ABSTRACT

The present invention provides a test strip for measuring a concentration of an analyte of interest in a biological fluid, wherein the test strip may be encoded with information that can be read by a test meter into which the test strip is inserted. In one embodiment, a first test strip comprises: a first measurement electrode connectable to a test meter; a first trace loop with a first associated resistance, where the first trace loop is connectable to the test meter; and a second trace loop with a second associated resistance, where the second trace loop is connectable to the test meter. The test meter is adapted to: receive the first test strip; connect to the first measurement electrode, the first trace loop, and the second trace loop; and obtain a first resistance ratio by comparing the first and second associated resistances.

REFERENCE TO RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 11/097,606, filed Apr. 1, 2005 (attorney docket No. WP 23094US/7404-675).

TECHNICAL FIELD OF THE INVENTION

The present invention relates to an apparatus for use in measuringconcentrations of an analyte in a biological fluid. The inventionrelates more particularly to a system and method for coding informationon a biosensor test strip.

BACKGROUND OF THE INVENTION

Measuring the concentration of substances in biological fluids is animportant tool for the diagnosis and treatment of many medicalconditions. For example, the measurement of glucose in body fluids, suchas blood, is crucial to the effective treatment of diabetes.

Diabetic therapy typically involves two types of insulin treatment:basal, and meal-time. Basal insulin refers to continuous, e.g.time-released insulin, often taken before bed. Meal-time insulintreatment provides additional doses of faster acting insulin to regulatefluctuations in blood glucose caused by a variety of factors, includingthe metabolization of sugars and carbohydrates. Proper regulation ofblood glucose fluctuations requires accurate measurement of theconcentration of glucose in the blood. Failure to do so can produceextreme complications, including blindness and loss of circulation inthe extremities, which can ultimately deprive the diabetic of use of hisor her fingers, hands, feet, etc.

Multiple methods are known for determining the concentration of analytesin a blood sample, such as, for example, glucose. Such methods typicallyfall into one of two categories: optical methods and electrochemicalmethods. Optical methods generally involve spectroscopy to observe thespectrum shift in the fluid caused by concentration of the analyte,typically in conjunction with a reagent that produces a known color whencombined with the analyte. Electrochemical methods generally rely uponthe correlation between a current (Amperometry), a potential(Potentiometry) or accumulated charge (Coulometry) and the concentrationof the analyte, typically in conjunction with a reagent that producescharge-carriers when combined with the analyte. See, for example, U.S.Pat. Nos. 4,233,029 to Columbus, 4,225,410 to Pace, 4,323,536 toColumbus, 4,008,448 to Muggli, 4,654,197 to Lilja et al., 5,108,564 toSzuminsky et al., 5,120,420 to Nankai et al., 5,128,015 to Szuminsky etal., 5,243,516 to White, 5,437,999 to Diebold et al., 5,288,636 toPollmann et al., 5,628,890 to Carter et al., 5,682,884 to Hill et al.,5,727,548 to Hill et al., 5,997,817 to Crismore et al., 6,004,441 toFujiwara et al., 4,919,770 to Priedel, et al., and 6,054,039 to Shieh,which are hereby incorporated herein by reference in their entireties.The biosensor for conducting the tests is typically a disposable teststrip having a reagent thereon that chemically reacts with the analyteof interest in the biological fluid. The test strip is mated to anondisposable test meter such that the test meter can measure thereaction between the analyte and the reagent in order to determine anddisplay the concentration of the analyte to the user.

It is common practice in such test meter/test strip systems to ensureproper identification of the test strip in order to ensure proper testresults. For example, a single test meter may be able to analyze severaldifferent types of test strips, wherein each type of test strip isdesigned to test for the presence of a different analyte in thebiological fluid. In order to properly conduct the test, the test metermust know which type of test is to be performed for the test stripcurrently in use.

Also, lot-to-lot variations in the test strips normally requirecalibration information to be loaded into the test meter in order toensure accurate test results. A common practice for downloading suchcalibration information into the test meter is the use of an electronicread-only memory key (ROM key) that is inserted into a socket of thetest meter. Because this calibration data may only be accurate for aparticular production lot of test strips, the user is usually asked toconfirm that the lot number of the test strip currently in use matchesthe lot number for which the ROM key was programmed.

Many other instances in which it is desirable to have informationrelating to the test strip are known to those having skill in the art.Prior art attempts to code information onto the test strip for readingby the test meter have suffered from many problems, including a severelylimited amount of information that can be coded and the use ofrelatively large amounts of test strip surface area for the informationcoding function.

Thus, a system and method are needed that will allow information to becoded onto a biosensor for reading of the information by the test meter.The present invention is directed toward meeting this need.

SUMMARY OF THE INVENTION

The present invention provides a test strip for measuring aconcentration of an analyte of interest in a biological fluid, whereinthe test strip may be encoded with information that can be read by atest meter into which the test strip is inserted.

In one form of the invention, a system for measuring a concentration ofan analyte of interest in a biological fluid is disclosed. The systemcomprises a test meter and a first test strip with a first maskconfiguration, a first resistive element, and a second resistiveelement. The first mask configuration comprises: a first measurementelectrode that is connectable to the test meter; a first trace loop witha first associated resistance and a first gap, where the first traceloop is connectable to the test meter; and a second trace loop with asecond associated resistance and a second gap, where the second traceloop is connectable to the test meter. The first resistive element isconductively connected to the first trace loop and bridges the firstgap, and the second resistive element is conductively connected to thesecond trace loop and bridges the second gap. The system furthercomprises a second test strip with a second mask configuration, a thirdresistive element, and a fourth resistive element, where the second maskconfiguration is substantially similar to the first mask configuration.The second mask configuration comprises: a second measurement electrodeconnectable to the test meter; a third trace loop with a thirdassociated resistance and a third gap, where the trace loop isconnectable to the test meter; and a fourth trace loop with a fourthassociated resistance and a fourth gap, where the fourth trace loop isconnectable to the test meter. The third resistive element isconductively connected to the third trace loop and bridges the thirdgap, and the fourth resistive element is conductively connected to thefourth trace loop and bridges the fourth gap. The test meter is adaptedto receive the first and second test strips, connect to the first andsecond measurement electrodes, and connect to the first and second traceloops. The test meter is further adapted to obtain a first resistanceratio by comparing the first and second associated resistances, connectto the third and fourth trace loops, and obtain a second resistanceratio by comparing the third and fourth associated resistances. The testmeter may be further adapted to correlate each of the first and secondresistance ratios to one or more predetermined values that correspond toinformation about the first and/or second strips.

In another form of the invention, a system for measuring a concentrationof an analyte of interest in a biological fluid is disclosed. The systemcomprises a test meter and a first test strip. The first test stripcomprises: a first measurement electrode connectable to the test meter;a first trace loop with a first associated resistance, where the firsttrace loop is connectable to the test meter; and a second trace loopwith a second associated resistance, where the second trace loop isconnectable to the test meter. The test meter is adapted to: receive thefirst test strip; connect to the first measurement electrode, the firsttrace loop, and the second trace loop; and obtain a first resistanceratio by comparing the first and second associated resistances.

In another form of the invention, a method for measuring a concentrationof an analyte of interest in a biological fluid is disclosed. The methodcomprises providing a test meter and providing a first test strip. Thefirst test strip comprises: a first measurement electrode connectable tothe test meter; a first trace loop with a first associated resistance,where the first trace loop is connectable to the test meter; and asecond trace loop with a second associated resistance, where the secondtrace loop is connectable to the test meter. The method furthercomprises: receiving the first test strip into the test meter;communicatively connecting the first measurement electrode, the firsttrace loop, and the second trace loop with the test meter; and obtaininga first resistance ratio by comparing the first and second associatedresistances.

In another form of the invention, a method for encoding informationreadable by a test meter onto a test strip, where the test strip adaptedfor measuring a concentration of an analyte of interest in a biologicalfluid, is disclosed. The method comprises selecting a first resistanceratio associated with a first word desired to be encoded on the teststrip and forming a measurement electrode on the surface of the teststrip substrate, where the measurement electrode is connectable to atest meter. The method further comprises forming a first electricaltrace and a second electrical trace on the surface of the test stripsubstrate, where the resistance of each of the first and secondelectrical traces are obtainable by the test meter, and where the ratioof the resistance of the first electrical trace and the resistance ofthe second electrical trace effectively matches the first resistanceratio.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be further described, by way of example only, withreference to the accompanying drawings, in which:

FIG. 1 is an exploded perspective view of a first typical test strip foruse in measuring the concentration of an analyte of interest in abiological fluid.

FIG. 2 is a perspective view of a second typical test strip for use inmeasuring the concentration of an analyte of interest in a biologicalfluid.

FIG. 3 illustrates a view of an ablation apparatus suitable for use withthe present invention.

FIG. 4 is a view of the laser ablation apparatus of FIG. 3 showing asecond mask.

FIG. 5 is a view of an ablation apparatus suitable for use with thepresent invention.

FIG. 6 is a schematic process flow diagram of a prior art process forverifying the applicability of the calibration data in the test meter tothe test strip currently inserted into the test meter.

FIG. 7 is a schematic process flow diagram of a first embodiment processof the present invention for verifying the applicability of thecalibration data in the test meter to the test strip currently insertedinto the test meter.

FIG. 8 is a schematic plan view of a second embodiment test stripelectrode and contact pad arrangement according to the presentinvention.

FIG. 9 is a schematic plan view the test strip electrode and contact padarrangement of FIG. 8 illustrating a modified trace.

FIG. 10 is a schematic plan view the test strip electrode and contactpad arrangement of FIG. 8 illustrating another modified trace.

FIG. 11 is a schematic plan view the test strip electrode and contactpad arrangement of FIG. 8 illustrating yet another modified trace.

FIG. 12 is a schematic plan view of a third embodiment test stripelectrode and contact pad arrangement according to the presentinvention.

FIG. 13 is a schematic plan view of a fourth embodiment test stripelectrode and contact pad arrangement according to the presentinvention.

FIG. 14 is a schematic plan view of a fifth embodiment test stripelectrode and contact pad arrangement according to the presentinvention.

FIG. 15 is a schematic plan view the test strip electrode and contactpad arrangement of FIG. 14 illustrating alternate resistive elements anda modified trace.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

For the purposes of promoting an understanding of the principles of theinvention, reference will now be made to the embodiment illustrated inthe drawings, and specific language will be used to describe thatembodiment. It will nevertheless be understood that no limitation of thescope of the invention is intended. Alterations and modifications in theillustrated device, and further applications of the principles of theinvention as illustrated therein, as would normally occur to one skilledin the art to which the invention relates are contemplated, are desiredto be protected. In particular, although the invention is discussed interms of a blood glucose meter, it is contemplated that the inventioncan be used with devices for measuring other analytes and other sampletypes. Such alternative embodiments require certain adaptations to theembodiments discussed herein that would be obvious to those skilled inthe art.

Although the system and method of the present invention may be used withtest strips having a wide variety of designs and made with a widevariety of construction techniques and processes, a typicalelectrochemical test strip is illustrated in FIG. 1, and indicatedgenerally at 10. Referring to FIG. 1, the test strip 10 comprises abottom substrate 12 formed from an opaque piece of 350 μm thickpolyester (such as Melinex 329 available from DuPont) coated on its topsurface with a 50 nm conductive (gold) layer (by sputtering or vapordeposition, for example). Electrodes, connecting traces and contact padstherefore are then patterned in the conductive layer by a laser ablationprocess. The laser ablation process is performed by means of an excimerlaser which passes through a chrome-on-quartz mask. The mask patterncauses parts of the laser field to be reflected while allowing otherparts of the field to pass through, creating a pattern on the gold whichis ablated where contacted by the laser light. The laser ablationprocess is described in greater detail hereinbelow. For example, working20, counter 22, dose sufficiency working 24, and dose sufficiencycounter 26 electrodes may be formed as shown and coupled, respectively,to measurement contact pads W, C, DW and DC. These contact pads providea conductive area upon the test strip 10 to be contacted by a connectorcontact of the test meter once the test strip 10 is inserted into thetest meter. As used herein, the phrase “measurement contact pad” isdefined as a contact pad on the test strip that is conductively coupledto a measurement electrode of the test strip and is a primary contactpad for measuring a characteristic of a body fluid sample, such assample size or the concentration of an analyte in the sample. As usedherein, the phrase “information contact pad” is defined as a contact padon the test strip that is not a measurement contact pad and is used forencoding information onto the test strip.

The bottom substrate 12 is then coated in the area extending over theelectrodes with a reagent layer 14 as a continuous, extremely thinreagent film. The reagent layer 14 is a stripe of approximately 6millimeters width across the substrate 12 in the region labeled “ReagentLayer” on FIG. 1. For example, this region may be coated at a wet-coatweight of 50 grams per square meter of coated surface area. The reagentstrip is dried conventionally with an in-line drying system where thenominal air temperature is at 110° C. The rate of processing isnominally 30-38 meters per minute and depends upon the rheology of thereagent.

The materials are processed in continuous reels such that the electrodepattern is orthogonal to the length of the reel, in the case of thesubstrate 12. Once the substrate 12 has been coated with reagent, thespacers 16 are slit and placed in a reel-to-reel process onto thesubstrate 12. Two spacers 16 formed from 100 μm polyester (for example,Melinex 329 available from DuPont) coated with 25 μm PSA (hydrophobicadhesive) on both the dorsal and ventral surfaces are applied to thebottom substrate 12, such that the spacers 16 are separated by 1.5 mmand the working, counter and dose sufficiency electrodes are centered inthis gap. A top foil layer 18 formed from 100 μm polyester coated with ahydrophilic film on its ventral surface (using the process described inU.S. Pat. No. 5,997,817) is placed over the spacers 16. The hydrophilicfilm is coated with a mixture of Vitel and Rhodapex surfactant at anominal thickness of 10 microns. The top foil layer 18 is laminatedusing a reel-to-reel process. The test strips can then be produced fromthe resulting reels of material by means of slitting and cutting.

Although the basic test strip 10 illustrated in FIG. 1 can provideaccurate measurements of blood glucose in a whole blood sample, it doesnot provide any means for the test meter into which it is inserted toidentify anything about the test strip. The present invention presentssystems by which information relating to the test strip can be codeddirectly onto the test strip itself, such that this information can beconveyed to a test meter into which the test strip is inserted.

One method of preparing a test strip encoded with information asdescribed herein is by the use of laser ablation techniques. Examples ofthe use of these techniques in preparing electrodes for biosensors aredescribed in United States Patent Application Publication Number2002/0192115, entitled “Biosensor,” filed May 25, 2001, and in U.S. Pat.No. 6,662,439, entitled “Laser Defined Features for Patterned Laminatesand Electrodes,” issued Dec. 16, 2003, both disclosures herebyincorporated herein by reference in their entireties. As used herein,the term “encode” is defined as to convert from one system ofcommunication into another and includes situations where particularaspects of a test strip are controlled or manipulated in a manner thatwill provide information to a test meter. The systems and methodsdisclosed herein include analog comparative methods and situations whereinformation is read by a test meter, conveyed to the test meter, andgleaned from the test strip.

It is desirable in the present invention to provide for the accurateplacement of the electrical components relative to one another and tothe overall biosensor. In another embodiment, the relative placement ofcomponents is achieved, at least in part, by the use of broad fieldlaser ablation that is performed through a mask or other device that hasa precise pattern for the electrical components. This allows accuratepositioning of adjacent edges, which is further enhanced by the closetolerances for the smoothness of the edges.

FIG. 2 illustrates a simple biosensor 401 useful for illustrating thelaser ablation process of the present invention, including a substrate402 having formed thereon conductive material 403 defining electrodesystems comprising a first electrode set 404 and a second electrode set405, and corresponding traces 406, 407 and contact pads 408, 409,respectively. The conductive material 403 may contain pure metals oralloys, or other materials, which are metallic conductors. Theconductive material is generally absorptive at the wavelength of thelaser used to form the electrodes and of a thickness amenable to rapidand precise processing. Non-limiting examples include aluminum, carbon,copper, chromium, gold, indium tin oxide (ITO), palladium, platinum,silver, tin oxide/gold, titanium, mixtures thereof, and alloys ormetallic compounds of these elements. In some embodiments, theconductive material includes noble metals or alloys or their oxides. Inother embodiments, the conductive material includes gold, palladium,aluminum, titanium, platinum, ITO and chromium. In still otherembodiments, the conductive material ranges in thickness from about 10nm to 80 nm. In further embodiments, the conductive material ranges inthickness from about 30 nm to 70 nm. In still further embodiments, theconductive material thickness equals approximately 50 nm. It isappreciated that the thickness of the conductive material depends uponthe transmissive property of the material and other factors relating touse of the biosensor.

While not illustrated, it is appreciated that the resulting patternedconductive material can be coated or plated with additional metallayers. For example, the conductive material may be copper, which isthen ablated with a laser into an electrode pattern; subsequently, thecopper may be plated with a titanium/tungsten layer, and then a goldlayer, to form the desired electrodes. In some embodiments, a singlelayer of conductive material is used, which lies on the base 402.Although not generally necessary, it is possible to enhance adhesion ofthe conductive material to the base, as is well known in the art, byusing seed or ancillary layers such as chromium nickel or titanium. Inother embodiments, biosensor 401 has a single layer of gold, palladium,platinum or ITO.

Biosensor 401 is illustratively manufactured using two apparatuses 410,410′, shown in FIGS. 3-5, respectively. It is appreciated that unlessotherwise described, the apparatuses 410, 410′ operate in a similarmanner. Referring first to FIG. 3, biosensor 401 is manufactured byfeeding a roll of ribbon 420 having an 80 nm gold laminate, which isabout 40 mm in width, into a custom fit broad field laser ablationapparatus 410. The apparatus 410 comprises a laser source 411 producinga beam of laser light 412, a chromium-plated quartz mask 414, and optics416. It is appreciated that while the illustrated optics 416 is a singlelens, in some embodiments optics 416 is a variety of lenses thatcooperate to make the light 412 in a pre-determined shape.

A non-limiting example of a suitable ablation apparatus 410 (FIGS. 3-4)is a customized MicrolineLaser 200-4 laser system commercially availablefrom LPKF Laser Electronic GmbH, of Garbsen, Germany, which incorporatesan LPX-400, LPX-300 or LPX-200 laser system commercially available fromLambda Physik AG, Göttingen, Germany and a chromium-plated quartz maskcommercially available from International Phototool Company, ColoradoSprings, Co.

For the MicrolineLaser 200-4 laser system (FIGS. 3-4), the laser source411 is a LPX-200 KrF-UV-laser. It is appreciated, however, that higherwavelength UV lasers can be used in accordance with this disclosure. Thelaser source 411 works at 248 nm, with a pulse energy of 600 mJ, and apulse repeat frequency of 50 Hz. The intensity of the laser beam 412 canbe infinitely adjusted between 3% and 92% by a dielectric beamattenuator (not shown). The beam profile is 27×15 mm² (0.62 sq. inch)and the pulse duration 25 ns. The layout on the mask 414 ishomogeneously projected by an optical elements beam expander,homogenizer, and field lens (not shown). The performance of thehomogenizer has been determined by measuring the energy profile. Theimaging optics 416 transfer the structures of the mask 414 onto theribbon 420. The imaging ratio is 2:1 to allow a large area to be removedon the one hand, but to keep the energy density below the ablation pointof the applied chromium mask on the other hand. While an imaging of 2:1is illustrated, it is appreciated that the any number of alternativeratios are possible in accordance with this disclosure depending uponthe desired design requirements. The ribbon 420 moves as shown by arrow425 to allow a number of layout segments to be ablated in succession.

The positioning of the mask 414, movement of the ribbon 420, and laserenergy are computer controlled. As shown in FIG. 3, the laser beam 412is projected onto the ribbon 420 to be ablated. Light 412 passingthrough the clear areas or windows 418 of the mask 414 ablates the metalfrom the ribbon 420. Chromium coated areas 424 of the mask 414 blocksthe laser light 412 and prevent ablation in those areas, resulting in ametallized structure on the ribbon 420 surface. Referring now to FIG. 4,a complete structure of electrical components may require additionalablation steps through a second mask 414′. It is appreciated thatdepending upon the optics and the size of the electrical component to beablated, that only a single ablation step or greater than two ablationsteps may be necessary in accordance with this disclosure. Further, itis appreciated that instead of multiple masks, that multiple fields maybe formed on the same mask in accordance with this disclosure.

Specifically, a second non-limiting example of a suitable ablationapparatus 410′ (FIG. 5) is a customized laser system commerciallyavailable from LPKF Laser Electronic GmbH, of Garbsen, Germany, whichincorporates a Lambda STEEL (Stable energy eximer laser) laser systemcommercially available from Lambda Physik AG, Göttingen, Germany and achromium-plated quartz mask commercially available from InternationalPhototool Company, Colorado Springs, Co. The laser system features up to1000 mJ pulse energy at a wavelength of 308 nm. Further, the lasersystem has a frequency of 100 Hz. The apparatus 410′ may be formed toproduce biosensors with two passes as shown in FIGS. 3 and 4. In certainembodiments, the optics of apparatus 410′ permit the formation of a10×40 mm pattern in a 25 ns single pass.

While not wishing to be bound to a specific theory, it is believed thatthe laser pulse or beam 412 that passes through the mask 414, 414′, 414″is absorbed within less than 1 μm of the surface 402 on the ribbon 420.The photons of the beam 412 have an energy sufficient to causephoto-dissociation and the rapid breaking of chemical bonds at themetal/polymer interface. It is believed that this rapid chemical bondbreaking causes a sudden pressure increase within the absorption regionand forces material (metal film 403) to be ejected from the polymer basesurface. Since typical pulse durations are around 20-25 nanoseconds, theinteraction with the material occurs very rapidly and thermal damage toedges of the conductive material 403 and surrounding structures isminimized. The resulting edges of the electrical components have highedge quality and accurate placement as contemplated by the presentinvention.

Fluence energies used to remove or ablate metals from the ribbon 420 aredependent upon the material from which the ribbon 420 is formed,adhesion of the metal film to the base material, the thickness of themetal film, and possibly the process used to place the film on the basematerial, i.e. supporting and vapor deposition. Fluence levels for goldon KALADEX® range from about 50 to about 90 mJ/cm², on polyimide about100 to about 120 mJ/cm², and on MELINEX® about 60 to about 120 mJ/cm².It is understood that fluence levels less than or greater than the abovementioned can be appropriate for other base materials in accordance withthe disclosure.

Patterning of areas of the ribbon 420 is achieved by using the masks414, 414′ and 414″. Each mask 414, 414′ and 414″ illustratively includesa mask field 422 containing a precise two-dimensional illustration of apre-determined portion of the electrode component patterns to be formed.FIG. 3 illustrates the mask field 422 including contact pads and aportion of traces. As shown in FIG. 4, the second mask 414′ contains asecond corresponding portion of the traces and the electrode patternscontaining fingers. As previously described, it is appreciated thatdepending upon the size of the area to be ablated, the mask 414 cancontain a complete illustration of the electrode patterns (FIG. 5), orportions of patterns different from those illustrated in FIGS. 3 and 4in accordance with this disclosure. It is contemplated that in oneaspect of the present invention, the entire pattern of the electricalcomponents on the test strip are laser ablated at one time, i.e., thebroad field encompasses the entire size of the test strip, asillustrated by mask 414″ in FIG. 5. In the alternative, and asillustrated in FIGS. 3 and 4, portions of the entire biosensor are donesuccessively.

While mask 414 will be discussed hereafter, it is appreciated thatunless indicated otherwise, the discussion will apply to masks 414′,414″ as well. Referring to FIG. 3, areas 424 of the mask field 422protected by the chrome will block the projection of the laser beam 412to the ribbon 420. Clear areas or windows 418 in the mask field 422allow the laser beam 412 to pass through the mask 414 and to impactpredetermined areas of the ribbon 420. As shown in FIG. 3, the cleararea 418 of the mask field 422 corresponds to the areas of the ribbon420 from which the conductive material 403 is to be removed.

Further, the mask field 422 has a length shown by line 430 and a widthas shown by line 432. Given the imaging ratio of 2:1 of the LPX-200, itis appreciated that the length 430 of the mask is two times the lengthof a length 434 of the resulting pattern and the width 432 of the maskis two times the width of a width 436 of the resulting pattern on ribbon420. The optics 416 reduces the size of laser beam 412 that strikes theribbon 420. It is appreciated that the relative dimensions of the maskfield 422 and the resulting pattern can vary in accordance with thisdisclosure. Mask 414′ (FIG. 4) is used to complete the two-dimensionalillustration of the electrical components.

Continuing to refer to FIG. 3, in the laser ablation apparatus 410 theexcimer laser source 411 emits beam 412, which passes through thechrome-on-quartz mask 414. The mask field 422 causes parts of the laserbeam 412 to be reflected while allowing other parts of the beam to passthrough, creating a pattern on the gold film where impacted by the laserbeam 412. It is appreciated that ribbon 420 can be stationary relativeto apparatus 410 or move continuously on a roll through apparatus 410.Accordingly, non-limiting rates of movement of the ribbon 420 can befrom about 0 m/min to about 100 m/min. In some embodiments, othernon-limiting rates of movement of the ribbon 420 can be from about 30m/min to about 60 m/min. It is appreciated that the rate of movement ofthe ribbon 420 is limited only by the apparatus 410 selected and maywell exceed 100 m/min depending upon the pulse duration of the lasersource 411 in accordance with the present disclosure.

Once the pattern of the mask 414 is created on the ribbon 420, theribbon is rewound and fed through the apparatus 410 again, with mask414′ (FIG. 4). It is appreciated, that alternatively, laser apparatus410 could be positioned in series in accordance with this disclosure.Thus, by using masks 414, 414′, large areas of the ribbon 420 can bepatterned using step-and-repeat processes involving multiple mask fields422 in the same mask area to enable the economical creation of intricateelectrode patterns and other electrical components on a substrate of thebase, the precise edges of the electrode components, and the removal ofgreater amounts of the metallic film from the base material.

The ability to code information directly onto the test strip candramatically increase the capabilities of the test strip and enhance itsinteraction with the test meter. For example, it is well known in theart to supply the test meter with calibration data applicable to anygiven manufacturing lot of test strips. Typically, this is done bysupplying a read-only memory key (ROM key) with each vial of teststrips, where the ROM key has encoded thereon the calibration dataapplicable to the test strips in the vial. Before using the test stripsfrom the vial, the user inserts the ROM key into a port in the testmeter so that the test meter may have access to this data whileperforming tests using the test strip. The quality of the measurementresult can be verified by allowing the meter to electronically assessthe applicability of the ROM key data to the test strip currentlyinserted into the meter, without the need for an optical reader to readbar code information on the test strip as has been taught in the priorart.

Current commercially-available products require the user to be involvedin verifying the correct ROM key has been inserted into the test meterfor the test strip currently being used. For example, FIG. 6 illustratesa typical prior art process for verifying the match between the ROM keydata and the test strip lot identification (ID) number. Prior toexecuting this process, the ROM key has been inserted into the testmeter, the ROM data has been loaded into the test meter, and the testmeter is turned off. The process begins by inserting a test strip (step100) into the test meter, which causes the test meter to automaticallyturn on (step 102). The test meter displays the lot ID of the currentlyloaded calibration data (step 104) in order to give the user the chanceto verify that this lot ID matches the lot ID printed on thevial/package (for example) containing a plurality of test strips fromthe same production lot as the test strip currently inserted into thetest meter.

Because the process relies upon the user to perform this check, there isno way to guarantee that it is done or if it is, that it is doneaccurately. The process of FIG. 6 therefore indicates an optional stepfor the user to compare the lot ID on the test meter display to the lotID on the test strip vial (step 106) and to determine (step 108) ifthere is a match. If the two lot IDs do not match, then the user shouldremove the test strip (step 110) and insert the ROM key that matches thetest strip vial into the test meter (step 112) so that the propercalibration code can be loaded into the test meter. The process wouldthen start over at step 100 with the insertion of the test strip. Onceit has been determined that the test meter's calibration code lot IDmatches the lot ID of the test strip (step 108), then the measurementsequence can continue by applying blood to the test strip (step 24) andbeginning the blood glucose measurement cycle (step 116).

It will be appreciated that responsibility for verification of theaccuracy of the measurement calibration data has been placed completelyin the hands of the user in the prior art process of FIG. 6. It issometimes encountered that users ignore stated use instructions providedwith the test strips. One such example is the removal of test stripsfrom a first vial that were manufactured in lot X and consolidatingthese test strips into a second vial containing test strips manufacturedin lot Y. Therefore, it is desirable to bring lot specific calibrationinformation to the individual test strip level instead of to the viallevel as is done in the prior art.

In order to remove the possibility of human error or neglect from theprocess, and to thereby improve the quality of the measurement, theinformation contact pads of the present invention allow the test meteritself to perform checks as to the applicability of the currently loadedcalibration data to the currently inserted test strip. A firstembodiment process of the present invention to allow the test meter toactively participate in such verification is illustrated in FIG. 7. Thesteps of the process of FIG. 7 that are identical to the correspondingsteps in FIG. 6 are numbered with the same reference designators.

Prior to executing this process, the ROM key has been inserted into thetest meter, the ROM data has been loaded into the test meter, and thetest meter is turned off. The process begins by inserting a test strip(step 100) into the test meter, which causes the test meter toautomatically turn on (step 102). The test meter then measures theconductivity between the various information and measurement contactpads on the test strip that have been designated for encodinginformation onto the test strip in order to ascertain the lot or familyID of the test strip (step 200). Depending upon the quantity ofinformation that may be encoded onto the test strip, it may or may notbe possible to code a unique production lot number onto the test strip.If there is not sufficient space for unique production lot IDs to beencoded, it is still possible to encode calibration family informationonto the test strip. For example, the test strips usable in the testmeter may be of two or more families where significant differences existbetween the family test strip designs. For example, two families may usea different reagent on the test strip. In such situations, the testmeter can still verify that the loaded calibration data matches the teststrip family encoded onto the test strip, even if it is not possible toverify the precise production lot of the test strip. Therefore, as usedherein, the phrase “lot ID” is intended to encompass any informationthat identifies a group to which the test strip or calibration databelongs, even if that group is not as small as a production lot of thetest strip.

Returning to the process of FIG. 7, the test meter compares (step 202)the lot ID of the calibration data stored within the ROM key currentlyinserted into the meter (or calibration data previously-loaded into thetest meter internal memory) to the lot ID read from the test strip. Ifthey do not match, the test meter displays the lot ID of the currentlyloaded calibration data (step 204) and a warning in order to give theuser the chance to insert a correct test strip or to insert a differentROM key into the test meter. Alternatively, the test meter may simplydisplay an error message to the user. The fact that the lot IDs do notmatch is flagged (step 206) in the test meter's result memory 208 sothat there is a record in the memory 208 that the measurement resultobtained is suspect in view of the discrepancy in the lot IDs.Alternatively, the user may be prohibited from running a test and theprocess may be aborted.

Because in some embodiments it is desired that the test meter not becompletely disabled if the lot IDs do not match, the process of FIG. 7indicates an optional step for the user to compare the lot ID on thetest meter display to the lot ID on the test strip vial (step 106) andto determine (step 108) if there is a match. If the two lot IDs do notmatch, then the user should remove the test strip (step 110) and insertthe ROM key that matches the test strip vial into the test meter (step112) so that the proper calibration code can be loaded into the testmeter. The process would then start over at step 100 with the insertionof the test strip.

Also optionally, if the test meter has the capacity to store more thanone calibration dataset within the meter's internal memory, then themeter may determine the multiple lot IDs of calibration data that may bestored within the test meter and automatically choose the calibrationdataset that matches the test strip currently inserted into the meter.The meter can then return to step 24.

Once it has been determined that the test meter's calibration code lotID matches the lot ID of the test strip (step 108), then the measurementsequence can continue by applying blood to the test strip (step 24) andbeginning the blood glucose measurement cycle (step 116). It will beappreciated that the process of FIG. 7 represents an improvement overthe prior art process of FIG. 6 in that the user is automatically warnedwhen the lot ID of the test strip does not match the lot ID of thecurrently-selected calibration dataset. Furthermore, if a test isconducted with this mismatched combination, then the result memorywithin the test meter is flagged to indicate that the result may not beas accurate as would be the case if the correct calibration dataset wereused.

As a further example of the usefulness of encoding information directlyonto the test strip, the present invention allows the test strip toactivate or deactivate certain features programmed into the test meter.For example, a single test meter may be designed to be used in severaldifferent geographic markets, where a different language is spoken ineach market. By encoding the test strips with information indicating inwhich market the test strips were sold, the encoded information cancause the test meter to display user instructions and data in a languagethat is appropriate for that market. Also, a meter may be designed forsale in a certain geographic market and it is desired that the meter notbe used with test strips obtained in a different geographic market (forexample when governmental regulations require the test strips sold inone geographic market to have different features than those sold inother geographic markets). In this situation, information coded onto thetest strip may be used by the test meter to determine that the teststrip did not originate in the designated geographic market andtherefore may not provide the features required by regulation, in whichcase the test may be aborted or flagged.

Further, a business model (subscription business model) may be appliedfor the distribution of test strips where proliferation of the teststrips into other sales channels is not desired. For example, users mayenroll into a subscription program in which they are provided with atest meter designed for use by subscription participants, and thesubscription participants may be provided with subscription test stripson a regular basis (for example by mail or any other convenient form ofdelivery). Using the techniques of the present invention, the“subscription test strips” may be encoded to indicate that they weresupplied to a subscription participant. For a variety of reasons, themanufacturer of the subscription test strips may not want thesubscription test strips to be sold in other channels of trade. One wayto prevent this is to design test meters provided to users who are notsubscription participants that will not work with subscription teststrips. Therefore, the present invention may be used to provide testmeters to subscription participants in the subscription business modelthat are programmed to accept subscription test strips encoded toindicate that they are delivered to a user on the basis of asubscription, while other test meters are programmed not to acceptsubscription test strips so encoded.

As a further example, the test meter can have certain functionalities(software- and/or hardware-implemented) designed into the meter that arenot active when the test meter is first sold. The performance of thetest meter can then be upgraded at a later date by including informationencoded on the test strips sold at that later time that will berecognized by the meter as an instruction to activate these latentfeatures. As used herein, the phrase “activating a latent feature of thetest meter” comprehends turning on a test meter functionality thatpreviously was not active, such that the test meter functionalitythereafter remains activated indefinitely (i.e. after the current testwith the present test strip is finished).

Another example of information that can be encoded onto the test stripusing the present invention is an indication of whether the test stripwas sold to the hospital market or to the consumer market. Having thisinformation may allow the test meter to take action accordingly, such asdisplaying user instructions in less detail for the hospitalprofessional. It will be appreciated by those skilled in the art that avariety of types of communication between the test strip and the testmeter may be facilitated by the information encoding provided by thepresent invention.

Systems and methods for encoding information onto a test strip aredepicted in FIGS. 8-15. These encoding systems and methods are usefulwhen used exclusively on a test strip, and can also be used inconjunction with other encoding systems and methods. Generally speaking,the encoding systems and methods depicted in FIGS. 8-15 provide for theresistance of at least one trace or trace loop, which is connected to apair of associated contact pads, to be varied between test stripsdepending on the information to be encoded on each individual teststrip. A test meter, in turn, measures the resistance of the trace ortrace loop between a particular pair of contact pads on an inserted teststrip, and decodes the resistance related information encoded on thetest strip. In general, the test meter can determine in a digital sensewhich connections either exist or do not exist, and can measure in ananalog sense the resistance between any connected contact pads. Theability for the test meter to obtain both digital and analog informationallows the systems and methods of the present invention to be combinedwith other encoding systems. When combined with other encoding systemsand methods, such as the encoding systems and methods disclosed in JP2000/000352034 A2 and EP 1152239A1, which are hereby incorporated hereinby reference in their entireties, the number of words that may beencoded on the test strip can be dramatically increased over that whichcan be encoded using the other system alone.

An alternate encoding scheme may also be used where the trace or traceloop resistance is ratioed, or proportionally compared, with at leastone other trace or trace loop resistance. This alternate encoding schemehas benefits in compensating for inconsistencies that result fromvariations in trace or trace loop resistance from test strip to teststrip.

In contrast to the encoding systems and methods of the presentinvention, some previous systems have examined test strip resistance asa fail-safe against inadvertent opens, scratches, or multiple pointdefects. Others have attempted to compensate for unwanted test striptrace resistance. Still other previous systems have merely determinedwhether a nontrivial trace resistance was present, and used theexistence or nonexistence of the nontrivial resistance as a binaryindicator of which of two types of strips was present—a strip intendedfor measurement or calibration purposes. In the systems that usedresistance as a binary indicator, the determination of whether or not aparticular trace had a nontrivial resistance was accomplished bycomparing a measured resistance to a near-zero threshold resistancevalue. If the measured resistance was above the threshold value, thetrace resistance was considered to be nontrivial, thereby indicating onetype of strip. If the measured resistance was below the threshold value,the trace resistance was considered to be trivial and essentially zero,and the other type of strip was indicated. Thus, the system onlydistinguished between resistance values that were essentially zero andthose that were not. Conversely, the systems and methods of the currentinvention are generally capable of distinguishing between at least twosubstantially non-zero resistance values.

In general, the systems and methods for encoding information on the teststrip as disclosed in the present invention are useful to: discriminatebetween specific types of test strips; determine whether the insertedtest strip matches a separate code key inserted into the test meter;encode calibration information directly onto the test strip; identifysignificant parameters related to the test strip such as country oforigin, destination, or particular test strip chemistry; and determinewhich reagent is on the test strip. The systems and methods of thepresent invention are further useful in encoding information on a teststrip that can be used for: choosing a language in which the test meterdisplays user operating instructions; determining if the test meter andtest strip were sold in the same geographic market; preventing use ofthe test strip by the test meter if the test strip is a subscriptiontest strip; activating a latent feature of the test meter; changing theuser operating instructions; or performing other functions as would beobvious to one of ordinary skill in the art.

A second embodiment test strip configuration that allows information tobe encoded directly onto the test strip is illustrated in FIG. 8 andindicated generally at 700. The test strip 700 may be formed generallyas described above with respect to the test strips 10 and 401, withworking 720, counter 722, dose sufficiency working 724, and dosesufficiency counter 726 electrodes formed as shown and coupled,respectively, to working electrode 721, counter electrode 723, dosesufficiency working electrode 725, and dose sufficiency counterelectrode 727 traces, which are further coupled, respectively, tomeasurement contact pads W, C, DW and DC. The test strip 700 furtherincludes working electrode 730 and counter electrode 732 sense traces,which are coupled to measurement contact pads WS and CS, respectively.The contact pads provide a conductive area upon the test strip 700 to becontacted by an electrical connector contact for the test meter once thetest strip 700 is inserted into the test meter. The electrical connectorallows electrical signals to be applied from the test meter to the teststrip and vice versa. The test strip may be formed with a sample inletin the distal end of the test strip (as shown in FIG. 8), or with thesample inlet on the side of the test strip (as shown in FIG. 1), by wayof example. The type of sample inlet is not related to the functionalityof the embodiments described herein.

Referring to the traces connected to contact pads W and WS, theresistance along three portions between contact pads W and WS may beevaluated by a test meter: the resistance along working electrode trace721 between contact pad W and the point where working electrode sensetrace 730 connects, the resistance along sense trace 730 between contactpad WS and the point where electrode sense trace 720 connects, and thetrace loop resistance between contact pads W and WS—“trace loop W-WS.”In the first instance, a test meter can use working electrode sensetrace 730 to measure the potential of working electrode trace 721 at thepoint where sense trace 730 connects to electrode trace 721 by using avoltage follower circuit or other similar method as known in the art(see, for example, the methods and circuits disclosed in co-pendingapplication Ser. No. 10/961,352, which has been incorporated byreference hereinabove). Since the potential and current flow at contactpad W can be directly measured by the test meter, the change inpotential, and thus the resistance, along working electrode trace 721between contact pad W and the point where working electrode sense trace730 intersects working electrode trace 721 can be calculated by the testmeter. The resistance along working electrode sense trace 730 can besimilarly calculated by the test meter.

Alternatively, the resistance of trace loop W-WS can be calculated bymeasuring the total change in potential between contact pads W and WSand the current flow therebetween. The calculated resistance along atrace loop includes the connector contact resistance between the testmeter and the contact pads, the trace loop resistance, and theresistance of any analog switches in the test meter's measurement path.In an example embodiment, the trace loop W-WS is comprised of goldconductive material and has a nominal resistance of approximately 287Ohms. In another example embodiment, the trace loop W-WS is comprised ofpalladium conductive material and has a nominal resistance ofapproximately 713 Ohms.

The resistance of a trace loop may be measured by AC or DC excitation.In one example embodiment, the W-WS loop resistance is measured by DCexcitation while the C-CS loop resistance is measured by AC excitation.Other example embodiments utilize varying combinations of AC and/or DCexcitation to measure trace and trace loop resistance on a test strip,some embodiments exclusively utilizing AC excitation with otherembodiments exclusively utilizing DC excitation.

Referring to the traces connected to contact pads C and CS, theresistance along counter electrode trace 723 between contact pad C andthe point where counter electrode sense trace 732 connects, theresistance along sense trace 732 between contact pad CS and the pointwhere electrode trace 723 connects, and the trace loop C-CS resistancebetween contact pads C and CS can each be determined by a test meter ina manner similar to that described above with respect to the tracesconnected to contact pads W and WS. In an example embodiment, the traceloop C-CS is comprised of gold conductive material and has a resistanceof approximately 285 Ohms. In another example embodiment, the trace loopC-CS is comprised of palladium conductive material and has a resistanceof approximately 712 Ohms.

Test strip 700 also includes information traces 734 and 736, which areconnected to information contact pads B1 and B2, respectively.Information traces 734 and 736 are further connected, respectively, todose sufficiency counter electrode trace 727 and counter electrode trace723. Not only can information contact pads B1 and B2 and theirassociated trace loops be used with the encoding systems and methodsillustrated in FIGS. 1-15 and described above, the various traceresistance values of trace loops DC-B1 and C-B2 can be used to furtherencode information onto test strip 700. For example, the resistancevalues of trace 734, trace 736, the portion of trace 727 between contactpad DC and the point where trace 734 connects, the portion of trace 723between contact pad C and the point where trace 736 connects, trace loopDC-B1, and trace loop C-B2 can all be individually measured and used toencode information on test strip 700 in a manner similar to thatdescribed above with respect to the traces connected to contact pads Wand WS.

Information digitally encoded on a test strip provides a limited numberof options to encode information, for example, the test strip may belimited to 2^(N) potential states or words, where N is the number ofinformation contact pads on the test strip. In contrast, the resistancemeasured by a test meter is generally not limited to discrete values andany value along a continuum of potential trace resistance values may bemeasured. Thus, the number of words or states encodable on a test stripusing a continuum of trace resistance values can exceed the number ofwords or states encodable on a test strip using discrete digital states,which generally only determine if a connection between two contact padsis present or not.

The number of potential words and the amount of information that can beencoded on a test strip using the resistance of test strip traces ortrace loops is typically limited by the ability to precisely manufacturea particular trace resistance and the ability to accurately measure thesame trace resistance. Given an ability to precisely control theresistance during manufacture and precisely measure a trace or traceloop resistance, a theoretically infinite amount of information can beencoded on a test strip, where each measurable resistance along thecontinuum corresponds to a different word or state. However, due toactual manufacturing and measurement capabilities, the number ofavailable resistance values along the continuum is frequentlyrestricted. To account for measurement and manufacturing errors, thenumber of available states along the continuum may be subdivided into anumber of discrete ranges, where each discrete range corresponds to adifferent word or state, and the range of resistance values associatedwith each range is approximately as large as the cumulative measurementand manufacturing errors. In one example embodiment, the information asto the number of discrete ranges or size of each discrete range may beprogrammed onto a ROM key that is inserted into the test meter.

The method used to measure resistance and other factors, such as thetemperature of the test strip and test meter, can also affect theresistance measured by the test meter and the minimum size of eachdiscrete range that may be used. For example, in one embodiment of thepresent invention the measured trace or trace loop resistance includesthe resistance of at least one analog switch internal to the test meter,where the analog switch resistance varies from 10 to 180 Ohms dependingon the temperature and manufacturing tolerances. If, for illustrativepurposes, it is assumed that the test meter has a resistance measurementaccuracy of +/−30 Ohms, then the smallest size for each discrete rangethat may be used to encode information onto the test strip is at least60 Ohms.

As stated above, one advantage of the trace or trace loop resistanceencoding systems and methods is that they can be used in conjunctionwith other systems. Combining trace loop resistance encoding with otherencoding methods can considerably increase the total number of wordsencodable on a test strip over that which can be encoded using the othermethods alone, even when limiting the available states along thecontinuum of possible resistance values to discrete ranges.

As an example encoding system and method utilizing discrete ranges ofresistances, it is assumed that the resistance along each of the W-WSand C-CS trace loops in FIG. 8 is limited to be within one of threemeasurable resistance ranges, represented by range numbers 1, 2, and 3.Thus, a total of nine different words can be encoded on test strip 700by measuring the resistance of trace loops W-WS and C-CS: WS1/CS1,WS1/CS2, WS1/CS3, WS2/CS1, WS2/CS2, WS2/CS3, WS3/CS1, WS3/CS2, andWS3/CS3. Combining this resistance encoding scheme with another encodingscheme, the total number of states encodable can be increased by afactor of nine. For example, JP 2000/000352034 A2 potentially disclosesa total of eight states encodable onto the side of a test strip with themeasurement electrode. Combining the current example with JP2000/000352034 A2 results in a total of 72 states that may be encodedonto a test strip. More generally, exclusively using the trace or traceloop resistance encoding systems and methods provides a total of R^(L)unique words (R being the number of resistance states or ranges, and Lbeing the number of trace loops) that may be encoded onto a test strip,while using the trace or trace loop resistance encoding system inconjunction with another encoding system provides an increase in thetotal words that may be encoded onto a test strip by a factor of R^(L)over the other encoding system.

In general, the resistance in a particular trace as measured by a testmeter varies, at least in part, with trace width, trace length, tracethickness, trace conductive material, trace temperature, and test meterswitch resistance. Factors such as the exact width, length, thicknessand conductive material of the trace can be controlled duringmanufacture, but manufacturing inconsistencies may result inunintentional variations in resistance resulting in trace resistancevalues different from what was intended. Furthermore, despite identicaltest strip mask configurations, these factors can further vary from teststrip to test strip and production lot to production lot. However, theratio of two trace or trace loop resistance values generally remainsrelatively consistent for a given test strip mask configuration despitethese manufacturing inconsistencies. Thus, a technique that may be usedby the test meter to counteract manufacturing inconsistencies is toratio two trace or trace loop resistance measurement values. Using thisor similar techniques, the test meter can effectively compensate forvariations in resistance by evaluating resistance ratios between tracesor trace loops, especially if necessary test meter analog switches arepaired by type, size, process and package.

As an example, manufacturing inconsistencies in the amount of conductivematerial deposited on the substrate can result in trace thicknessvarying from test strip to test strip while trace width and lengthremain relatively constant for a given test strip mask configuration.However, these inconsistencies in the amount of conductive materialdeposited tend to vary slowly enough such that trace thickness tends tobe uniform over a single test strip while varying from test strip totest strip. Thus, the ratio of trace resistance between two traces onthe same test strip will remain essentially constant despitemanufacturing inconsistencies.

Variations in trace width, length, thickness, and the materialcomposition of the trace may be manipulated to control individual traceresistance values during manufacture since, as stated above, thesecharacteristics affect the resistance of each trace. For example, theresistance of the C-CS trace loop can be reduced by either increasingthe width of the counter electrode trace 723 or the counter electrodesense trace 732, or by decreasing the overall length of the loop.Similarly, the C-CS loop's resistance can be increased by decreasing thewidth of either trace 723 or 732, or by increasing the effective overalllength of the loop.

Alternate embodiments utilize different test strip mask configurations.The number, location, or particular type of electrode traces to whichthe information traces may be connected can vary with the onlylimitation being that the functionality of the test strip can not becompromised by, for example, connecting any of the electrodes orelectrode traces to one another.

Referring now to FIG. 9, therein is depicted an alternate exampleembodiment test strip 700′, which is similar to test strip 700 except asnoted below. Working electrode sense trace 730′ is wider than workingelectrode sense trace 730. In this example alternate embodiment, theW-WS trace loop resistance in test strip 700′ is less than the W-WStrace loop resistance in test strip 700. Similarly, the ratio of theW-WS loop resistance to C-CS loop resistance in test strip 700′ is lessthan the ratio of the W-WS loop resistance to C-CS loop resistance intest strip 700 due to the increased width in sense trace 730′. Thus,information is encoded on test strips 700 and 700′ by varying tracewidth. A test meter may therefore distinguish between test strip 700 andtest strip 700′ by, for example, measuring the absolute resistance intrace loop W-WS, measuring the absolute resistance in a segment of traceloop W-WS, or by determining the ratio of the W-WS trace loop resistanceand the C-CS trace loop resistance.

Referring now to FIG. 10, therein is depicted yet another exampleembodiment test strip 700″, which is similar to test strip 700 except asnoted below. Test strip 700″ includes alternate working electrode sensetrace 730″. Sense trace 730″ differs from sense trace 730 in that sensetrace 730″ is shorter than sense trace 730. In this example alternateembodiment, the W-WS trace loop resistance in test strip 700″ is lessthan the W-WS trace loop resistance in test strip 700. Similarly, theratio of the W-WS loop resistance to C-CS loop resistance in test strip700″ is less than the ratio of the W-WS loop resistance to C-CS loopresistance in test strip 700 due to the decreased length in sense trace730″. Thus, information is encoded on test strips 700 and 700′ byvarying trace length. A test meter may therefore distinguish betweentest strip 700 and test strip 700″ by, for example, measuring theabsolute resistance in trace loop W-WS, measuring the absoluteresistance in a segment of trace loop W-WS, or by determining the ratioof the W-WS trace loop resistance and the C-CS trace loop resistance.

FIG. 11 depicts still another example embodiment test strip 700′″, whichis a variation of test strip 700 and differs from test strip 700 asnoted below. Test strip 700′″ includes counter electrode sense trace732′, which has a longer and narrower electrical path length and,consequently, a higher resistance than sense trace 732. In this examplealternate embodiment, the C-CS trace loop resistance in test strip 700′″is greater than the C-CS trace loop resistance in test strip 700.Similarly, the ratio of the W-WS loop resistance to C-CS loop resistancein test strip 700′″ is less than the ratio of the W-WS loop resistanceto C-CS loop resistance in test strip 700 due to the increased length insense trace 732′. Thus, information is encoded on test strips 700 and700′ by varying trace length. A test meter may therefore distinguishbetween test strip 700 and test strip 700′″ by, for example, measuringthe absolute resistance in trace loop C-CS, measuring the absoluteresistance in a segment of trace loop C-CS, or by determining the ratioof the W-WS trace loop resistance and the C-CS trace loop resistance.

A third embodiment test strip configuration is illustrated in FIG. 12and indicated generally at 800. The test strip 800 is generally similarto test strip 700 described above except as otherwise indicated, withworking electrode 820, counter electrode 822, dose sufficiency workingelectrode 824, dose sufficiency counter electrode 826, working electrodesense trace 830, and counter electrode sense trace 832 formed as shownand coupled, respectively, to measurement contact pads W, C, DW, DC, WSand CS. In contrast to test strip 700, test strip 800 includesinformation trace 834 and information trace 836, which are connected toinformation contact pads B1 and B2, respectively, and further connectedto each other. These contact pads provide a conductive area upon thetest strip 800 to be contacted by an electrical connector contact of thetest meter once the test strip 800 is inserted into the test meter.

In the depicted embodiment of the test strip 800, information trace 834and information trace 836 combine to provide a trace loop B1-B2 betweeninformation contact pads B1 and B2. Resistance of at least oneinformation trace 834 and 836 can be varied to encode information inaddition to that which may be encoded using trace loops W-WS and C-CS.When inserted into a test meter, test strip 800 is distinguishable fromtest strip 700 since contact pads DC and B1 are not connected, sincecontact pads C and B2 are not connected, and since contact pads B1 andB2 are connected. Test strip 800 is further distinguishable from teststrip 700 based on the measured value of the B1-B2 loop resistance.Generally speaking, the test meter can determine in a digital sensewhich connections either exist or do not exist, and can measure in ananalog sense the resistance between any connected contact pads. Theresistance of information traces 834 and 836 can be varied duringmanufacture by varying the width, thickness, length, or materialutilized to construct information traces 834 and 836.

A fourth embodiment test strip configuration is illustrated in FIG. 13and indicated generally at 900. The test strip 900 may be formed withworking electrode 920, dose sufficiency working electrode 924,information trace 934 and information trace 936 being formed as shownand coupled, respectively, to measurement contact pads W and DW, andinformation contact pads B1 and B2. Additionally, the test strip 900includes counter electrode 922 and dose sufficiency counter electrode926 connected, respectively to counter electrode trace 923 and dosesufficiency counter electrode trace 927, which in turn are furtherconnected to measurement contact pads C and DC, respectively. Similar tothe test strips 700 and 800, the contact pads provide a conductive areaupon the test strip 900 to be contacted by an electrical connectorcontact of the test meter once the test strip 900 is inserted into thetest meter.

In the example embodiment test strip 900, information trace 934 iselectrically connected to dose sufficiency counter electrode trace 927,and information trace 936 is electrically connected to counter electrodetrace 923. These electrical connections provide additional trace loopswhere the resistance may be measured between contact pads DC and B1, andC and B2. When connected to a test meter, the lack of electricalconnection between contact pads B1 and B2, the presence of an electricalconnection between contact pads B1 and DC, and the presence of anelectrical connection between B2 and C each separately be used to encodeinformation and distinguish test strip 900 from test strip 800.Additionally, the resistance along dose sufficiency counter electrodetrace 927, information trace 934, information trace 936, and counterelectrode trace 923 can further encode additional information concerningtest strip 900.

Furthermore, when compared with test strip 700, information traces 934and 936 are longer and have more resistance than information traces 734and 736. Thus, the DC-B1 and C-B2 trace loop resistances in test strip900 are, respectively, greater than the DC-B1 and C-B2 trace loopresistances in test strip 700. Thus, a test meter may distinguishbetween test strip 900 and test strip 700 by, for example, measuring theabsolute resistance in trace loops DC-B1 or C-B2, or by comparing theresistance ratios of either trace loops DC-B1 or C-B2 to one another orto other trace loops, such as trace loops W-WS or C-CS.

Turning now to FIGS. 14 and 15, therein is depicted an fifth embodimenttest strip 1000 that allows information to be encoded directly on thetest strip. The test strip 1000 may be formed with working electrode1020, dose sufficiency working electrode 1024, working electrode sensetrace 1030, counter electrode sense trace 1032, information trace 1034,and information trace 1036 formed as shown and coupled, respectively, tomeasurement contact pads W, DW, WS and CS, and information contact padsB1 and B2. Additionally, counter electrode 1022 and dose sufficiencycounter electrode 1026 are connected, respectively, to counter electrodetrace 1023 and dose sufficiency counter electrode trace 1027, which arein turn further connected, respectively, to measurement contact pads Cand DC. Information trace 1034 includes resistive element 1038 and isconnected to dose sufficiency counter electrode trace 1027. Informationtrace 1036 includes resistive element 1040 and is connected to counterelectrode trace 1023. The contact pads provide a conductive area uponthe test strip 1000 to be contacted by an electrical connector contactof the test meter once the test strip 1000 is inserted into the testmeter.

As depicted in FIGS. 14 and 15, trace loops DC-B1 and C-B2 are formedbetween measurement pads DC and B1, and C and B2, respectively. Asdescribed above, the resistance of trace loops DC-B1 and C-B2 can becontrolled during manufacture by varying the width, thickness, length,or material of the trace loops. However, having a large number ofdifferent test strip mask configurations in order to provide a largenumber of encoded words or states can be difficult and expensive duringmanufacture. One method by which the total number of test strip maskconfigurations may be reduced is to use a single mask configuration witha location along a trace where a resistive element can be included andintegrated into the trace. This method can be extended to integratingmultiple resistive elements into one or more traces. During manufacture,the resistance of a particular trace can be controlled by varying theresistance of the resistive element, or elements, included in aparticular trace, thus providing a simple and convenient manner tocontrol trace or trace loop resistance.

As an illustrative example, test strip 1000 in FIG. 14 utilizes afilm-type resistive element 1038 in information trace 1034. Thus, theoverall resistance in both information trace 1034 and trace loop B1-DCincludes the resistance of resistive element 1038. Similarly, theoverall resistance in both information trace 1036 and trace loop C-B2includes the resistance of resistive element 1040. During manufacture,the test strip 1000 may be initially formed using a test strip maskconfiguration with gaps in information traces 1034 and 1036. Later,resistive elements 1038 and 1034 are placed to span the gaps ininformation traces 1034 and 1036, respectively.

Now referring to FIG. 15, the test strip 1000′ depicts an embodimentwhere the DC-B1 trace loop resistance in FIG. 15 differs from the DC-B1trace loop resistance in FIG. 14, while the C-B2 trace loop resistancein FIG. 15 is equivalent to the C-B2 trace loop resistance in FIG. 14.The test strip 1000′ utilizes a relatively similar basic overall maskconfiguration as the test strip 1000 with gaps initially formed ininformation traces 1034 and 1036′ and with information trace 1036′ beinglonger than information trace 1036. In contrast to the test strip 1000,the gaps in test strip 1000′ are spanned by a conductive ink to formresistive elements 1038′ and 1040′. The conductive ink will be assumedfor this example to have less resistance for a given length than thefilm-type resistive elements used in FIG. 14. The resistance ofresistive element 1038′ is less than the resistance of resistive element1038, thus, the resistance of trace 1034 in FIG. 15 is less than theresistance of trace 1034 in FIG. 14. However, the increased length oftrace loop C-B2 and the increased length of resistive element 1040′result in the resistance of trace loop C-B2 in FIG. 15 equaling theresistance in trace loop C-B2 in FIG. 14. Thus, a test meter candistinguish between test strip 1000 and test strip 1000′ by measuring,for example, the resistance in trace 1034, the resistance in trace loopDC-B1 in, or the ratio of trace loop DC-B1 resistance and trace loopC-B2 resistance.

Resistive elements 1038, 1038′, 1040 and 1040′ may be comprised ofdifferent conductivity materials as are commonly known in the art formodifying trace resistance. These materials include conductive ink,screen printing thick film hybrid resistors, and standard fixed valuethick or thin film resistors.

In general, the total number of possible states that may be encoded on atest strip using the system and methods illustrated in FIGS. 16-23 anddescribed above is limited by the space available on the test stripsurface or materials available for manipulating trace or trace loopresistance; the ability to accurately control the resolution of theconductive features on the test strip, such as trace or trace loop size,shape, and placement; and the ability to accurately measure theresistance values on the test strip. An enhanced ability to accuratelycontrol trace geometry decreases the manufacturing related variation intrace resistance and allows additional words or states to be encoded ona test strip for a given test strip size and shape. Similarly, anenhanced ability to accurately control trace geometry allows for anincreased number of traces and information contact pads to be placed ona test strip, thereby allowing additional words or states to be encodedon a test strip for a given test strip size and shape.

It should be noted that the ability to precisely control trace geometryand increase the trace and contact pad densities as achieved in thepresent invention through the use of the laser ablation processrepresent a significant advancement over the prior art. The laserablation process described hereinabove allows for resolution of teststrip conductive features not previously achievable using prior arttechniques such as screen printing and photolithography. Because ofthis, relatively large quantities of data can be coded onto the teststrip when the conductive features are formed using the laser ablationprocess. For example, published European patent application EP 1 024 358A1 discloses a system which uses up to 35 contact pads on a single teststrip; however, the density of features is so low that the inventors areforced to contact only five of those contact pads at any one time. Notonly does this require much more test strip surface area than thepresent invention to form the same number of contact pads, but it isimpossible for the test meter to measure the resistance between each ofthe contact pads because the test meter is never in contact with morethan five of the contact pads at any one time. The tight control offeature dimensions enabled by the laser ablation process of the presentinvention allows for the use of trace and contact pad densities neverbefore achieved in the art.

It should also be appreciated that the term trace loop is not intendedto be limiting and does not imply a particular trace geometry, such as acircular path, and includes any portion of an electrical pathway alongwhich resistance can be determined.

It should be further appreciated that test strip characteristics bywhich a test meter can distinguish between two or more test strips arecharacteristics that can be utilized to encode information on a teststrip.

All publications, prior applications, and other documents cited hereinare hereby incorporated by reference in their entirety as if each hadbeen individually incorporated by reference and fully set forth.

While the invention has been illustrated and described in detail in thedrawings and foregoing description, the description is to be consideredas illustrative and not restrictive in character. Only the illustratedembodiments, and certain other embodiments deemed helpful in furtherexplaining how to make or use the illustrated embodiments, have beenshown. All changes and modifications that come within the spirit of theinvention are desired to be protected.

1. A system for measuring a concentration of an analyte of interest in a biological fluid, comprising: a test meter; a first test strip with a first mask configuration, a first resistive element, and a second resistive element, said first mask configuration comprising: a first measurement electrode connectable to said test meter, a first trace loop with a first associated resistance and a first gap, said first trace loop connectable to said test meter, and a second trace loop with a second associated resistance and a second gap, said second trace loop connectable to said test meter; wherein said first resistive element is conductively connected to said first trace loop and bridges said first gap; and wherein said second resistive element is conductively connected to said second trace loop and bridges said second gap; a second test strip with a second mask configuration, a third resistive element, and a fourth resistive element, said second mask configuration being substantially similar to said first mask configuration, said second mask configuration comprising: a second measurement electrode connectable to said test meter, a third trace loop with a third associated resistance and a third gap, said third trace loop connectable to said test meter, and a fourth trace loop with a fourth associated resistance and a fourth gap, said fourth trace loop connectable to said test meter; wherein said third resistive element is conductively connected to said third trace loop and bridges said third gap; and wherein said fourth resistive element is conductively connected to said fourth trace loop and bridges said fourth gap; and wherein said test meter is adapted to: receive said first and second test strips, connect to said first and second measurement electrodes, connect to said first and second trace loops, obtain a first resistance ratio by comparing said first and second associated resistances, connect to said third and fourth trace loops, and obtain a second resistance ratio by comparing said third and fourth associated resistances.
 2. The system of claim 1, wherein said first resistance ratio and said second resistance ratio are different.
 3. The system of claim 1, wherein: said test meter is adapted to determine whether said first resistance ratio correlates to a predetermined value when said test meter receives said first test strip, and said test meter is adapted to determine whether said second resistance ratio correlates to a predetermined value when said test meter receives said second test strip.
 4. The system of claim 3, wherein: said test meter tests the biological fluid for the analyte of interest if said first resistance ratio correlates to said predetermined value, and said test meter tests the biological fluid for the analyte of interest if said second resistance ratio correlates to said predetermined value.
 5. The system of claim 3, wherein: said test meter inhibits testing of the biological fluid for the analyte of interest if said first resistance ratio correlates to said predetermined value, and said test meter inhibits testing of the biological fluid for the analyte of interest if said second resistance ratio correlates to said predetermined value.
 6. The system of claim 3, wherein: said test meter records information relating to said first test strip if said first resistance ratio correlates to said predetermined value, and said test meter records information relating to said second test strip if said second resistance ratio correlates to said predetermined value.
 7. The system of claim 1, wherein: said test meter compares said first resistance ratio with at least two discrete, non-overlapping ranges, when said test meter receives said first test strip, and said test meter compares said second resistance ratio with said at least two discrete, non-overlapping ranges, when said test meter receives said second test strip.
 8. The system of claim 1, wherein: said first resistance ratio correlates to calibration information associated with said first test strip, and said second resistance ratio correlates to calibration information associated with said second test strip.
 9. The system of claim 1, wherein said first mask configuration further comprises a fifth trace loop with a fifth associated resistance and a fifth gap, said fifth trace loop connectable to said test meter, wherein said fifth resistive element is conductively connected to said fifth trace loop and bridges said fifth gap; wherein said test meter is adapted to connect to said fifth trace loop and obtain a third resistance ratio by comparing said first and fifth associated resistances.
 10. The system of claim 9, wherein said test meter is adapted to determine whether said third resistance ratio correlates to a predetermined value when said test meter receives said first test strip.
 11. A system for measuring a concentration of an analyte of interest in a biological fluid, comprising: a test meter; a first test strip, comprising: a first measurement electrode connectable to said test meter, a first trace loop with a first associated resistance, said first trace loop connectable to said test meter, and a second trace loop with a second associated resistance, said second trace loop connectable to said test meter; and wherein said test meter is adapted to: receive said first test strip, connect to said first measurement electrode, said first trace loop, and said second trace loop, and obtain a first resistance ratio by comparing said first and second associated resistances.
 12. The system of claim 11, wherein said test meter is adapted to measure said first and second associated resistances.
 13. The system of claim 11, wherein said first resistance ratio is configured to correlate to a predetermined value.
 14. The system of claim 11, wherein said test meter is adapted to determine whether said first resistance ratio correlates to a predetermined value.
 15. The system of claim 14, wherein said test meter is adapted to test the biological fluid for the analyte of interest when said first resistance ratio correlates to said predetermined value.
 16. The system of claim 14, wherein said test meter is adapted to inhibit testing of the biological fluid for the analyte of interest when said first resistance ratio correlates to said predetermined value.
 17. The system of claim 14, wherein said test meter is adapted to record information relating to said first test strip when said first resistance ratio correlates to said predetermined value.
 18. The system of claim 11, wherein said test meter is adapted to compare said first resistance ratio with at least two discrete, non-overlapping ranges, and wherein said first resistance ratio falls within a first one of said discrete ranges.
 19. The system of claim 11, wherein said first trace loop comprises a first material and said second trace loop comprises a second material different from said first material.
 20. The system of claim 11, wherein: said first and second associated resistances are different; said first trace loop comprises a first characteristic length, width, and thickness; said second trace loop comprises a second characteristic length, width, and thickness; and at least one of said first characteristic length, width, and thickness differs from a corresponding one of said second characteristic length, width, and thickness.
 21. The system of claim 11, wherein said first associated resistance and said second associated resistance correlate to calibration information associated with said first test strip.
 22. The system of claim 11, further comprising a first measurement electrode trace conductively connected to said first measurement electrode, wherein said first trace loop comprises at least a portion of said first measurement electrode trace.
 23. The system of claim 11, wherein a portion of said first trace loop comprises a material with first resistive qualities; and the remaining portion of said first trace loop comprises a different material with second resistive qualities different from said first resistive qualities.
 24. The system of claim 11, further comprising: a second test strip, comprising: a second measurement electrode connectable to said test meter, a third trace loop with a third associated resistance, said third trace loop connectable to said test meter, and a fourth trace loop with a fourth associated resistance, said fourth trace loop connectable to said test meter; and wherein said test meter is adapted to: receive said second test strip, connect to said second measurement electrode, said third trace loop, and said fourth trace loop, and obtain a second resistance ratio by comparing said third and fourth associated resistances.
 25. The system of claim 24, wherein said first and second resistance ratios are different.
 26. The system of claim 24, wherein: said test meter is adapted to determine whether said first resistance ratio correlates to a predetermined value, and said test meter is adapted to determine whether said second resistance ratio correlates to a predetermined value.
 27. The system of claim 26, wherein: said test meter is adapted to test the biological fluid for the analyte of interest when said first resistance ratio correlates to said predetermined value, and said test meter is adapted to test the biological fluid for the analyte of interest when said second resistance ratio correlates to said predetermined value.
 28. The system of claim 26, wherein: said test meter is adapted to inhibit testing of the biological fluid for the analyte of interest when said first resistance ratio correlates to said predetermined value, and said test meter is adapted to inhibit testing of the biological fluid for the analyte of interest when said second resistance ratio correlates to said predetermined value.
 29. The system of claim 26, wherein: said test meter is adapted to record information relating to said first test strip when said first resistance ratio correlates to said predetermined value, and said test meter is adapted to record information relating to said first test strip when said second resistance ratio correlates to said predetermined value.
 30. The system of claim 24, wherein: said test meter is adapted to compare said first resistance ratio with at least two discrete, non-overlapping ranges, and wherein said first resistance ratio falls within a first one of said discrete ranges, and said test meter is adapted to compare said second resistance ratio with said at least two discrete, non-overlapping ranges, and wherein said second resistance ratio falls within a second one of said discrete ranges.
 31. The system of claim 24, wherein: said first associated resistance and said second associated resistance correlate to calibration information associated with said first test strip, and said third associated resistance and said fourth associated resistance correlate to calibration information associated with said second test strip.
 32. The system of claim 24, wherein: said first and third associated resistances are different; said first trace loop comprises a first characteristic length, width, and thickness; said third trace loop comprises a third characteristic length, width, and thickness; and at least one of said first characteristic length, width, and thickness differs from a corresponding one of said third characteristic length, width, and thickness.
 33. The system of claim 24, wherein: said first test strip comprises: a first mask configuration with a first gap in said first trace loop and a second gap in said second trace loop, a first resistive element conductively connected to said first trace loop and bridging said first gap, and a second resistive element conductively connected to said second trace loop and bridging said second gap; said second test strip comprises: a second mask configuration with a third gap in said third trace loop and a fourth gap in said fourth trace loop, a third resistive element conductively connected to said third trace loop and bridging said third gap, and a fourth resistive element conductively connected to said fourth trace loop and bridging said fourth gap; and wherein said first mask configuration is substantially similar to said second mask configuration.
 34. The system of claim 33, wherein said first resistive element has an associated resistance and said third resistive element has an associated resistance, and wherein said first resistive element associated resistance is different from said third resistive element associated resistance.
 35. The system of claim 11, wherein said first test strip comprises a third trace loop with a third associated resistance, said third trace loop connectable to said test meter, and wherein said test meter is adapted to connect to said third trace loop and obtain a second resistance ratio by comparing said first and third associated resistances.
 36. The system of claim 35, wherein said test meter is adapted to determine whether said second resistance ratio correlates to a predetermined value. 